Background: The recommendation for carotid-femoral pulse wave velocity (cfPWV) is to use a calliper to measure the aortic length as a straight line. In adults, it has been shown that tape follows the body contours potentially making the distance longer - ultimately a higher cfPWV - interpreted as a higher aortic stiffness. Our objective was to investigate to what extent a tape measurement is influenced by abdominal obesity in children and adolescents. Methods: In a cross-sectional design, 100 obese patients with age 10-18 years were compared to 50 healthy control individuals. CfPWV was measured by applanation tonometry. The aortic length was determined with tape and a calliper (distance-tape and distance-calliper). The bias of the tape measurements was calculated as distance-tape minus distance-calliper. Results: The bias of the tape measurements (mean±SD) was significant in both the obese (δ 14.6±11.2mm, P<0.0001) and the control group (δ 5.7±5.8mm, P<0.0001), and showed a linear relationship with waist-height ratio in the obese group (obese: β=96.9, CI: 75.3-118.5, P<0.0001). Likewise, cfPWV was significantly higher when tape was used for the distance measurements in both groups (P values <0.0001). In multiple regression, however, cfPWV for both tape and calliper were significantly lower in the obese compared to the control group (P values <0.01). Conclusions: The bias of the tape measurements was related to the degree of abdominal obesity. Our results emphasize the importance of the use of a calliper when evaluating cfPWV in obese children and adolescents.